clash between acronym and twocolumn

Hi,

as the following example shows, the expansion of acronyms in twocolumn
mode leads to an ugly clash when the full form exceeds the column width.
How can this situation be avoided?

%% =====================================================================
 % !Mode:: "TeX:UK:UTF-8"
 % !TEX program = LuaLaTeX
 % !BIB program = biblatex
 % --------------------------------------------------------------------

\NeedsTeXFormat{LaTeX2e}
\documentclass[british,final,twocolumn]{scrbook}

\usepackage{polyglossia,%foreign language support
            acronym,% handles acronyms
            microtype,%micro-typesetting
            siunitx,%correct typesetting of units
            widetext,%switch between onecolumn and twocolumn without
pagebreak
            hyperref}%hyperrefs in PDF, must be last package called

\newcommand{\skalar}[1]{\ensuremath{#1}}

\title{Example}
\author{I, Me and Myself}
\date{\today}

\begin{document}

\frontmatter
\maketitle

\mainmatter

\chapter{Microscopy}\index{microscope|(}

\section{Light microscopy beyond the \textsc{Abbe} limit}

The following techniques are deterministic:
\begin{description}
  \item[\acf{STED}\index{STED}]{Since in a confocal microscope the lens
projecting the \acs{laser} light onto the specimen shows diffraction,
spot size is limited to about \qty{200}{nm}, this limits the resolution
of the confocal microscope. In \acs{STED}-microscopes, two \acs{laser}
beams are coupled into the microscope, one to excite fluorescence and
one to stimulate the emission of fluorescent light. Stimulated emission
returns the electron from the excited S\textsubscript{1} state to a
higher vibrational level of the ground state S\textsubscript{0}, the
emitted light is therefore red-shifted compared to that produced by
fluorescence (do not mix up stimulated emission, which is reversible,
with irreversible bleaching). The emission-stimulating beam has low
intensity in the centre but high intensity in the periphery, the higher
the power of this beam, the smaller the dark spot in the centre. Thus
fluorescence is observed only in a spot much smaller than the
diffraction spot. The new resolution becomes:
      \begin{equation}
         \Delta d = \frac{\lambda}{2 n \sin{\alpha} \sqrt{1 + I/I_
\mathrm{sat}}}
      \end{equation}
      with \skalar{I} the intensity of the emission stimulating beam and
\skalar{I_\mathrm{sat}} the saturation intensity (intensity that reduces
fluorescence probability by \qty{63}{\%} in the order of \unit{GW/cm},
achieved for very short times (\unit{ps})) for the emission stimulating
beam. This is a constant which depends on the fluorescent dye. Of
course, the second beam is also diffraction-limited, however, the
intensity of that beam is much higher than that of the exciting beam; in
addition, photons from the second beam can turn off several dye
molecules. As a result, the excited dye molecules are concentrated in a
spot much smaller than the diffraction limit, the size of this spot is
controlled by the intensity of the second beam. With this technique a
resolution down to \qty{2.5}{nm} has been achieved and several \qty{10}
{nm} are routine. \num{200} images can be taken per second. \textsc
{Stefan W. Hell} received the \textsc{Nobel}-Prize in Chemistry in \num
{2014} for this technique, together with \textsc{R.E. Betzig} and
\textsc{W. E. Moerner}. MINIFLUX (minimal photon flux) is a newer
development using the same principle, it allows \qty{2}{nm} resolution
in all three dimensions and with two colours. }
  \item[\acf{SSIM}]{The sample is illuminated with patterned light,
often stripes. The pattern is moved over the sample and the resulting
signal measured repeatedly (about 15 times). The interaction of sub-
diffraction details in the sample and the pattern of the light produces
a moiré-effect, whose \acf{FT} can be used to extract the structure of
the sample with twice the resolution obtainable by standard microscopy.
With light patterned in three dimensions, 3D images of the object can be
obtained. Newer approaches use a sinusoidal light pattern with a peak
intensity that exceeds the saturation of the dye used.  }
\end{description}

\backmatter
\appendix

\chapter{Appendix}

\section*{Acronyms used}

\begin{acronym}
   \acro{FT}{\textsc{Fourier} transform}{, modern way of obtaining
spectra fast and with high resolution}
   \acro{GSD}{ground state depletion}{, method of super-resolution
microscopy}
   \acro{laser}{light amplification by stimulated emission of radiation}
{, method to produce collimated, monochromatic, linear polarised light
beams},
   \acro{SPEM}{saturated pattern excitation}{, method of super-
resolution microscopy}
   \acro{SPIM}{single plane imaging microscopy}{, technique to increase
contrast in fluorescence microscopy by eliminating out-of-focus light}
   \acro{SSIM}{saturated structured illumination microscopy}{, method of
super-resolution microscopy}
   \acro{STED}{Stimulated emission depletion}{, method of super-
resolution microscopy}
\end{acronym}

\end{document}